Vasculogenesis is the formation of blood vessels and a primary vascular network in the developing embryo. Several growth factors including vascular endothelial growth factor (VEGF), fibroblast growth factor (FGF), Angiopoeitin, and their receptors Flk-1, Flt-1, Tie1, and Tie2 have been identified as being important mediators of these events. Despite our increasing knowledge of these growth factors and their receptors, much less is known about the factors which regulate vascular-specific gene expression during this process. The long term goal of this project is to understand the transcriptional regulation of vasculogenesis. The Ets genes are a family of transcription factors that regulate developmental processes and cellular differentiation. Several vascular-specific genes have recently been shown to have evolutionary conserved binding sites for Ets factors, which are critical for endothelial-specific gene expression. In particular, there are conserved Ets sites within the promoters of the Tie1 and Tie2 genes, which are necessary for vascular directed expression of these genes. NERF is a novel member of the Ets family which is expressed in endothelial cells and regulates the Tie1 and Tie2 genes. A novel chicken Ets factor, CAM-Ets4, which is highly homologous to NERF, is enriched in the developing blood vessels of the chicken chorioallantoic membrane (CAM). Aberrant NERF gene expression leads to the impaired formation of vascular tubes and channels in an in vitro matrigel model of angiogenesis. The hypothesis for these studies is that selected members of the Ets factor family and in particular NERF, are critical regulators of vascular development and endothelial function. The Specific Aims are to (1) Determine the temporal, spatial, and cellular expression pattern of NERF during development, and cellular differentiation (2) Determine the effects of altered NERF gene expression on endothelial function and vasculogenesis, and (3) further characterize the chicken NERF homologue during blood vessel development in the chicken. The methods used to achieve these specific aims include in situ hybridization, immunohistochemistry, embryonic stem cell differentiation models, DNAseI footprinting, Electrophoretic mobility shift assays, in vitro and in vivo models of blood vessel development, transgenic animals, and retroviral gene delivery. A better understanding of the transcriptional mediators of blood vessel development will not only provide new clues for the etiology of developmental defects in vasculogenesis, but also provide new therapeutic avenues for regulating blood vessel development or angiogenesis in disease states such as cancer, or coronary ischemia.